Acyloxybenzenesulfonic acid salts are used as bleach activators in detergents. European Patent Application No. 0 355 384 A1 discloses a procedure for preparing 4-acyloxybenzenesulfonic acid salts by reacting 4-hydroxybenzenesulfonic acid salts with an anhydride and a carboxylic acid. An acyloxybenzenesulfonic acid salt is isolated from the reaction mixture. After termination of the reaction, the acyloxybenzenesulfonic acid salt is washed with a hydrophilic solvent such as an alcohol. Such a procedure should not be used to prepare an alkali metal salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate because the intermediate [(1-oxyalkanoyl)amino]alkanoic acid can cyclize to form an acyl lactam which is not useful as a bleach activator and must be removed from the product. Additional purification steps would also reduce the yield of the product.
European Patent Application No. 0 105 672 A1 discloses a one-pot method of preparing an acyloxybenzene sulphonate salt wherein sodium 4-hydroxybenzenesulfonate reacts simultaneously with acetic anhydride and a carboxylic acid. The separation and recycling of the excess carboxylic acid is accomplished by washing with a hydrophobic solvent such as ether or hexane. A disadvantage of this procedure is that the intermediate, sodium 4-hydroxybenzenesulfonate, is insoluble in the hydrophobic solvents, and therefore, remains in the product when the reaction is incomplete. An acyloxybenzene sulphonate salt prepared according to European Patent Application No. 0 105 672 A1 does not satisfy the requirements of high-percent-yield and high purity. A further disadvantage is that the sodium 4-hydroxybenzenesulfonate has to be finely ground which is a tedious and cost-intensive process in order to achieve a complete reaction to give the acyloxybenzene sulphonate salt. Otherwise, a part of the intermediate product, 4-hydroxybenzenesulfonate, remains in the final product. Moreover, hydrophobic solvents such as ether or hexane should not be used to purify crude preparations of an alkali metal salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate because the intermediate [(1-oxyalkanoyl)amino]alkanoic acid is not soluble in hydrophobic solvents, and thus, would remain in the product.
Accordingly what is needed is a process to prepare high yields of a purified alkali metal salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate in one reaction vessel without isolation of intermediates. Moreover, the intermediate products such as sodium 4-acetoxybenzenesulfonate and [(1-oxyalkanoyl)amino]alkanoic acid should not remain in the final product. In addition, it would be advantageous to accomplish isolation of the product by direct evaporation of reaction solvent.